Manufacture of cables sheathed with lead base alloy



C. J. SNYDER MANUFACTURE OF CABLES SHEATHED April 18, 1950 WITH LEAD BASE ALLOY Filed June 4, 1948 INVENTOR Clef/270273 J Snyder BY GM clMM (ab-3 ATTORNEYS Patented Apr. 18, 1950 MANUFACTURE OF CABLES SHEATHED WITH LEAD BASE ALLOY Clermont J. Snyder, Hastings on Hudson, N. Y.,

assignor to Anaconda Wire and Cable Company, a corporation of Delaware Application June 4, 1948, Serial No. 31,038

3 Claims. 1

Main power distribution cables are almost invariably sheathed with a lead base alloy. The physical properties required of such sheaths approach the maximum that can be developed in lead base alloys. The sheath must be strong to withstand, for prolonged periods and without distortion, the hydrostatic pressure of the oil with which the cable insulation generally is impregnated, when the cable is run vertically for a considerable distance, and to withstand the superatmospheric gas pressure that quite often is maintained within power cables. It must have a, high resistance to creep, so that prolonged stresses will not cause it to become deformed. In addition, it must have high resistance to fatigue to be able to withstand repeated fiexure caused by expansion and contraction of the cable as it heats and cools with variations in the power loading. It is of the first order of importance that these properties be developed uniformly throughout the length of the cable, for even only one short weak or brittle section can be responsible for a sheath failure that ruins the entire length.

The present invention is direction to the provision of an improved method for insuring development of optimum physical properties uniformly throughout long lengths of cables sheathed with heat-treatable lead base alloys. The best cable sheaths are made from alloys which become hardened and otherwise develop maximum physical properties when heated. to an elevated temperature and then quenched; and the method of the invention involves flowing a hot liquid, heated to the quenching temperature of such alloy, over the cable sheath, thereby bringing the sheath uniformly to the desired quenching temperature, and directly thereafter quenching the sheath with cold water.

Lead base alloys containing 0.01% to 1% arsenic are representative of the best heat-treatable cable sheath alloys thus far developed. However, these as well as other lead base alloys which become hardened upon heating to an elevated temperature and then quenching are quite sensitive to variations in the temperature from which the alloy is quenched. This sensitivity manifests itself in the development of quite different degrees of strength and hardness as a result of rather small variations in the temperature of the alloy immediately prior to quenching. Considerable difficulty heretofore has been encountered in heat-treating lead base alloy cable sheaths so as to develop high physical properties uniformly throughout long lengths of the cable, and to avoid sections in the length of the cable that are undesirably hard and brittle, or unde sirably soft and weak.

Lead base alloy cable sheaths are formed by extrusion of the hot alloy about the cable, and it has been the practice heretofore to heat treat such sheaths by spraying with water as the cable,

freshly sheathed with still hot lead alloy, emerges from the lead press. This procedure has the advantage of minimizing the extent to which the cable must be handled, and more important, minimizing the extent to which the sheath must be mechanically worked by repeatedly winding it on and cit" cable reels, which may have an adverse effect on the physical properties of the sheath. It has been found that this practice effectively hardens the sheath, but does not do so uniformly. The sheath almost invariably has sections along its length where it is too hard and poorly resistant to fatigue, or where it is too soft and of low tensile strength. As a practical matter it is impossible to extrude the lead sheath at a uniform and constant temperature, so that the temperature from which it is quenched varies over a considerable range. This is due to the fact that the extrusion operation, while theoretically continuous, is not practically so. It is necessary periodically to replenish the charge of lead in the lead press, and the fresh charge of lead may begin to be extruded at a considerably higher or lower temperature than the preceding charge. Furthermore, when a new charge of lead is being introduced into the press, the extrusion operatime must stop momentarily, and the short length of cable between the lead press and the quenching water cools slowly, sometimes almost to room temperature. This section of the cable then does not become hardened by the quenching treatment. Furthermore, it is not as a practical matter possible to maintain the temperature of the die block of the lead press nearly so constant as is necessary to secure truly uniform heat treatment of the sheath, even during the periods when the press is for all practical purposes operating continuously. The die block temperature should ordinarily be quite close to 400 F., but in practice it varies all the way from 375 F to 450 F., and even beyond this range.

I have discovered that very uniform hardening of lead base alloy cable sheaths over long lengths of cable may be attained by passing the cable through a hot liquid, the temperature of which is closely controlled substantially at the desired quenching temperature, and quenching the cable sheath directly after it has been brought substantially to the temperature of the hot liquid. The invention therefore involves passing the sheathed cable, preferably as it emerges from the lead press, through a spray or flowing stream of? hot liquid substantially at the quenching temperature of the alloy, thereby to bring the sheath uniformly to that temperature. Directly thereafter the cable is passed through a spray or flowing stream of cold water. In this manher, the temperature from which the sheath is quenched is kept uniform, and as a result it is uniformly hardened and its other desired physical properties are equally uniformly developed.

A particularly advantageous embodiment of the invention is described below with reference to the accompanying drawing, the single figure of which shows a suitable arrangement of appa ratus for carrying out the new method.

The lead alloy sheath is applied to theeable: in a lead press, of which only the die block I (through which the cable passes and in which the sheath actually is formed) is shown in the drawing. The sheathed cable 2 emerges more or less continuously from this die block, in the directionindicated by the arrow. It will be assumed, for the purpose of the following description, that the cable sheath is composed of ajlead base alloycontaining 010l% to 1% of arsenic, and which is heat treated to develop optimum physical properties by heating to a temperature in the range from 350F. to'5725 F., followed by quenching in cold Water. The actual magnitude of the quenching temperature may vary considerably, within the range stated, depending upon the way in which it is desired to have the physical, properties improved. However, whatever quenching temperature within thisrange is chosen, itushould be very closely controlled (within i F.) to insure uniformity in theproperties vof the sheath throughout. the length of the cable.

A vessel 3 containingha body 4 of liquid heated to thedesired quenching temperature (say 450 F.).,is locatednearthe side of the lead pressfrom whichthe sheathedcable 2 emerges. Any material that is a stable liquid at. the, required temperature maybe used. Afused salt, such as amixture of potassium nitrate and sodium nitrite whichmeltsat. about 310 F., is eminently satisfactory. Oils that are stable at this temperature may be used if desired, as .wellas other .organic liquids thatcanbe heat d withoutdecomposition to the quenching. temperature of the cable sheath alloy. .Fusedsaltshave the advantageoi being particularly stable atthe temperatures involved, and maybe used atany temperature within the range ,from. 350 F. to 525 F. Oils .have the limitationof being most suitable for use at the temperatures in the lowerpartof this range (say up to47.5.F.),. but theyihavethe advantage of leaving a lubricatingfilmonthe cable sheath, .making it unnecessary (if a suitableoil isused) toapplyany otherlu-bricant to the sheathafter ithas beenheat treated.

Thetemperature of the fusedsalt or other hot liquid lismaintained at the desired temperature by arr-immersion typeelectric heating unitr5. A thermocouple 6 immersed .in thehot liquid is connected to a temperature indicator and controller .1, by means of whichthe power supplied to the heating-elementfrom.apower supplyline 8 .isregulated in accordance with the temperature indications of the thermocouple. The design and construction of the temperature indicator andcontroller i is not a part of the present invention. Any of the commercially available instruments of this character may be employed. However, the thermocouple and controller should be sufiiciently sensitive so as'to maintain the temperature of the hot liquid 45 within ilo and preferably even within :5" F. Very close control is important in order to insure a high degree of uniformityin the physical properties developed by the heat treatment of the cable sheath.

A submerged pump 9 driven by an electric motor delivers a steady stream of the hot liquid through thepipe H! to sprays H directed at the sheathed cable 2. The hot liquid wets the sheath and brings it uniformly to-the-optimum-quenching 4 temperature. Experiments have shown that it does not particularly matter whether the cable sheath as it emerges from the lead press is at a temperature higher or lower than that of the hot liquid, and, therefore, whether the hot liquid cools the cable sheath somewhat, or heats it. The important thing is that the hot liquid brings the cable sheath uniformly to an optimum temperature for quenching to develop the desired physical properties in the cable sheath.

Excess hot liquid draining from the cable is collected in a funnel-like trough I2 and delivered again to the body of such liquid in the vessel 3. A. wiper 13 in the form of an asbestos cord wrapped several times about the cable and tied to the end. of the trough l2 may be provided-to wipe off excess hot liquid as the cable moves in the, direction indicated by the arrow.

Directly after the cable has been sprayed withhot liquid, it passes under a spray it of cold water delivered through apipe I5 from a water supply main is, whereby the cable sheath is quenched about to room temperature. Water draining from the cable collects in a second trough-like funnel ii and is passed thence to waste. The hot liquid spray ii and the cold water spray l4 should be arranged with but a very short space between them--preferably only a few inchesso that there is little opportunity for the cable sheath to cool slowly in .the interval of its passage from the former tothe latter. Such arrangement insures that the cable sheath will in fact bequenched from, or very nearly from, the temperature to which it is brought by the hot liquid spray. Further, it insures against any soft spots resulting when forward. motion of the cable ceases for a while (as when the lead pressis being refilled with lead), and consequent slow coolingof the cable sheath at the section that happens then to be between the, hot liquid spray and the cold water spray.

The above-described, arrangement for flowing a hot liquid at a carefully controlled optimum quenching temperature over the cable sheath alloy, and then directly thereafter quenching the sheath, has the effect of insuring that quench ing isaccomplished from, a. uniformly maintained temperature. Asa result, the physicalproperties ofthesheath are ,very uniform throughout the lengthof the cable. The variationsin physi* cal properties from one part to another of the cable that result when .it is quenched directly as it emerges" from the ,dieblockare for the most part eliminated. Asindicated. above, these variations are due to the fact that the temperature of the cable sheath coming fromthe die block cannot as-a practical matter be maintained uniform enough to insure development of uniform properties upon quenching; whereasthe arrangement of the inventioninsures that any important variations in the quenching temperature are eliminated. Whether-the cable is too hot as it emerges from the die block, or too cold, it is first brought to the proper quenching temperature, and then almost-immediately is quenched. The physical properties are not noticeably different when the, hot liquid cools the cable sheath from a somewhat higher temperature than when the hot'liquid heats the cable sheath from a lower temperature. Evidentlyit is only necessary that the hotliquid bring the cable sheath uniformly to a substantially. constant optimum temorder to secure uniform development .of the de- 5 sired improved properties throughout the length of the cable.

In place of spraying the hot liquid and the quenching water on the cable, the apparatus might be arranged to immerse the cable successively in these liquids. Such an arrangement, however, is not particularly desirable, because it requires bending the cable first down into the hot liquid bath, then up from it and down again into the quenching water. Even this limited amount of mechanical working of the sheath is undesirable, especially while it is hot, because it leads to excessive grain growth and a lowering of the yield strength of the lead base alloy. Accordingly it is much preferable to flow or spray both the hot liquid and the quenching water onto the sheath while the latter moves forward in a substantially straight or very gently curved path, with but little or no bending.

The use of a hot liquid is much preferable to other arrangements for bringing the cable sheath to the optimum quenching temperature. For example, a gas burner or induction heating coil might be used to heat the sheath to the quenching temperature, but such an arrangement is not reliable for insuring that the cable sheath will be brought to a uniform quenching temperature. The extent to which the sheath is heated by such apparatus in passing through it depends too much on its temperature as it enters the burner or heating coil. It is very difficult, therefore, to control the sheath temperature, as it passes from such heating apparatus to the quenching medium, within the close limits that are necessary to insure uniform development of high physical properties throughout long lengths of the cable. This is especially so when (as is preferred to avoid excessive mechanical working of the sheath) the heat treatment is performed as the cable emerges from the lead press by which the sheath is extruded in place.

It has been found that by the method of the invention the uniformity with which desired physical properties are developed in long lengths of cable is very greatly increased as compared with the other methods heretofore proposed and em ployed for such purpose. The actual magnitude of the physical properties is controlled by suitably selecting the quenching temperature from Within the range from 350 F. to 525 F., and the uniformity with which the desired properties are developed is assured by the close control of this temperature within i10 F. of the desired value.

I claim:

1. In the manufacture of cable sheathed with a lead base alloy which becomes hardened upon heating to a temperature in the range from 350 F. to 525 F. and then quenching, including passing the cable through a lead press and extruding a sheath of the lead base alloy thereon, the improvement which comprises substantially continuously passing the cable with the extruded sheath thereon through a flowing hot liquid maintained at a substantially constant predetermined temperature in said range, maintaining the sheathed cable in said flowing hot liquid for a sufficient period of time to increase the temperature of portions of the sheath that are cooler than the liquid and to cool portions of the sheath that are hotter than the liquid so as to bring all portions of the sheath along its length substantially to the temperature of the liquid, and passing the cable after emergence from said flowing liquid and while its sheath is still substantially at the temperature of said hot liquid into and ,i; soft in comparison with the main portion of said sheath.

2. in the manufacture of sheathed with a lead base alloy containing 9.01% to 1% arsenic, including passing the cable through a lead press and extruding a sheath of the lead base alloy thereon, the improvement which comprises substantially continuously passing the cable with the extruded sheath thereon through a flowing hot liquid maintained at a substantially constant i'; predeterm ned temperature in the range from 35% F. to 525 F., maintaining the sheath d cable in said flowing hot liquid for a sufficient period of time to increase the temperature of portions of the sheath that are cooler than the liquid and to cool portions of the sheath that are hotter than the liquid so as to bring all portions of the along its length substantially to the temperature of the liquid, and passing the cable after emergence from said flowing liquid and while its sheath is still substantially at the temperature of said hot liquid into and through a flowing stream of cold quenching liquid, whereby the sheath is uniformly hardened and is substantially free from areas along its length that are either relatively hard or relatively soft in comparison with the main portion of said sheath.

3. In the manufacture of cable sheathed with a lead base alloy which becomes hardened upon heating to a temperature in the range from 350 F. to 525 F. and then quenching, including passing the cable through a lead press and extruding a sheath of the lead base al oy thereon, the improvement which comprises substantially continuously passing the cable with the extruded sheath thereon through a flowing hot liquid maintained at a substantially constant predetermined temperature in said range, the temperature of the liquid being maintained within :10 F. of said predetermined temperature, maintaining the sheathed cable in said flowing hot liquid for a sufficient period of time to increase the temperature of portions of the sheath that are cooler than the liquid and to cool portions of the sheath that are hotter than the liquid so as to bring all portions of the sheath along its length substan tially to the temperature of the liquid, and passing the cable after emergence from said flowing liquid and while its sheath is still substantially at the temperature of said hot liquid into and through a flowing stream of cold quenching liquid, whereby the sheath is uniformly hardened and is substantially free from areas along its length that are either relatively hard or relatively soft in comparison with the main portion of said sheath.

CLERMONT J. SNYDER.

REFERENCES CITED The following references are of record in the 85 file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Steel and Its Heat Treatment, by Bullens, published by John Wiley 8.: Sons Inc., N. Y., 19f13, 5 pp. 438-439. 

1. IN THE MANUFACTURE OF CABLE SHEATHED WITH A LEAD BASE ALLOY WHICH BECOMES HARDENED UPON HEATING TO A TEMPERATURE IN THE RANGE FROM 350* F. TO 525*F. AND THEN QUENCHING, INCLUDING PASSING THE CABLE THROUGH A LEAD PRESS AND EXTRUDING A SHEATH OF THE LEAD BASE ALLOY THEREON, THE IMPROVEMENT WHICH COMPRISES SUBSTANTIALLY CONTINUOUSLY PASSING THE CABLE WITH THE EXTRUDED SHEATH THEREON THROUGH A FLOWING HOT LIQUID MAINTAINED AT A SUBSTANTIALLY CONSTANT PREDETERMINED TEMPERATURE IN SAID RANGE, MAINTAINING THE SHEATHED CABLE IN SAID FLOWING HOT LIQUID FOR A SUFFICIENT PERIOD OF TIME TO INCREASE THE TEMPERATURE OF PORTIONS OF THE SHEATH THAT ARE COOLER THAN THE LIQUID AND TO COOL PORTIONS OF THE SHEATH THAT ARE HOTTER THAN THE LIQUID SO AS TO BRING ALL PORTIONS OF THE SHEATH ALONG ITS LENGTH SUBSTANTIALLY TO THE TEMPERATURE OF THE LIQUID, AND PASS- 